The present invention relates generally to polymer-clay nanocomposites comprising a matrix polymer and a layered clay material. The polymer-clay nanocomposites comprising the layered clay material may be processed under normal conditions while achieving low haze and improved oxygen barrier properties. This invention further relates to articles produced from the polymer-clay nanocomposites and processes relating to the nanocomposites.
Thermoplastic materials are being increasingly used in the packaging of beverages and perishable foods. Plastics are often the material of choice for food and beverage packaging because of their clarity, flexibility, toughness, high gas barrier, lighter weight, processability and high gloss.
Polymer composites comprising a layered clay material having platelet particles have potential for improved properties, including increased gas barrier, heat deflection temperature, and modulus. However, it has been found that films and articles made from polymer-clay nanocomposites often exhibit increased haze. The origin of this haze is not definitive, but platelet-particle agglomerates, impurities in the clay, crystalline haze, surface inhomogeniety all may contribute to increased haze. The impurities associated with montmorillonite clay, such as quartz, can not be modified to be compatible with the nylon resin molecules. Upon blow molding of the nanocomposite materials in the container fabricating process, voids will be generated around the inorganic particles. The voids may contribute to the haze. Furthermore, processes that include a high degree of orientation, or stretching of a material, often lead to the presence of voids and increased haze. For applications where clarity is important, such as beverage packaging, including beer packaging, films, etc., presence of voids and haze hinders aesthetic appeal and also may significantly affect physical properties of interest, such as gas barrier.
The presence of voids and haze in structures, particularly oriented structures containing polymer-clay composites make such structures less applicable for aesthetic and functional reasons. It is desirable, therefore, to significantly reduce the haze/voids of articles made from polymer-clay platelet particle nanocomposites.
Thus, there remains a need for polymer-clay nanocomposites that result in reduced haze and voids in articles made from such nanocomposites. There is also a need for articles and structures, particularly oriented monolayer and/or multilayer structures, comprising the nanocomposite material.
The present invention is generally related to polymer-clay nanocomposites. The nanocomposites of this invention result in an acceptable and reduced level of haze and voids, and improved physical properties afforded by the incorporation therein of a layered clay material comprising platelet particles. The reduced level of haze and voids are achieved by reducing the quartz content in the layered clay material.
As embodied and broadly described herein, this invention, in one embodiment, relates to a polymer-clay nanocomposite comprising a melt processible matrix polymer and a layered clay material having less than about 2.0% by weight of quartz, based on the weight of the clay material.
In another embodiment, the present invention relates to a multi-layer article having low haze comprising: (a) at least two structural polymer layers preferably comprising poly(ethylene terephthalate) (PET), or a copolymer thereof; and (b) at least one barrier layer disposed between the at least two structural layers comprising a melt processible matrix polyamide and incorporated therein a layered clay material having less than about 2.0% by weight of quartz, based on the weight of the clay material.
In yet another embodiment, the present invention relates to a process for preparing a polymer-clay nanocomposite comprising the steps of: (i) forming a concentrate comprising an oligomeric resin and a layered clay material having less than about 2.0% by weight of quartz, based on the weight of the clay material; and (ii) melt mixing the concentrate with a melt processible matrix polymer to form a polymer-clay nanocomposite.
In yet another embodiment, the present invention relates to a process for reducing haze in an article having a nanocomposite material comprising: (i) preparing a polymer-clay nanocomposite comprising the step of melt mixing a melt processible matrix polymer and a layered clay material having less than about 2.0% by weight of quartz, based on the weight of the clay material, to form a polymer-clay nanocomposite; and (ii) molding an article from the nanocomposite material, wherein the article has a haze which is at least about 4 percent lower than that of an article formed from a nanocomposite having unpurified clay therein.
Additional advantages of the invention will be set forth in part in the detailed description, including the figures, which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory of preferred embodiments of the invention, and are not restrictive of the invention, as claimed.